An AC-DC power converter includes a rectifying unit for generating a rectified voltage, an output stage for converting the rectified voltage into a DC voltage for a load, a controller for controlling the output stage, and a start-up circuit. The start-up circuit includes a start-up voltage generator coupled to the rectifying unit and configured to generate a start-up voltage from the rectified voltage and to output the start-up voltage to the controller to provide power for operation of the controller before the output stage starts outputting power. The start-up voltage generator includes a first depletion mode transistor having a first terminal configured to receive the rectified voltage, a second terminal configured to output at least partially the start-up voltage, and a gate terminal which is grounded.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An AC-DC power converter, comprising: a rectifying unit configured to rectify an AC voltage to a rectified voltage; an output stage coupled to the rectifying unit and configured to convert the rectified voltage into a DC voltage for a load; a controller coupled to the output stage and configured to control the output stage; and a start-up circuit comprising a start-up voltage generator which is coupled to the rectifying unit and configured to generate a start-up voltage from the rectified voltage and to output the start-up voltage to the controller to provide power for operation of the controller before the output stage starts outputting power; wherein the start-up voltage generator comprises a first depletion mode transistor having a first terminal configured to receive the rectified voltage, a second terminal configured to output at least partially the start-up voltage, and a gate terminal configured to receive a ground voltage throughout an entirety of a power-up of the AC-DC power converter from a powered-down state to a steady-state.
2. The AC-DC power converter of claim 1 , wherein the start-up voltage generator further comprises a resistor coupled between the second terminal of the first depletion mode transistor and a ground, the gate terminal of the first depletion mode transistor coupled to the ground.
3. The AC-DC power converter of claim 1 , wherein the first depletion mode transistor is configured to generate the start-up voltage at the second terminal.
4. The AC-DC power converter of claim 1 , wherein the first depletion mode transistor is configured to generate a first voltage which is a fraction of the start-up voltage at the second terminal; and the start-up voltage generator further comprises a second depletion mode transistor configured to generate a second voltage which is another fraction of the start-up voltage.
5. The AC-DC power converter of claim 4 , wherein the second depletion mode transistor has: a gate terminal coupled to the second terminal of the first depletion mode transistor, a first terminal coupled to receive the rectified voltage, and a second terminal configured to output a voltage which is a sum of the first and second voltages.
6. The AC-DC power converter of claim 5 , wherein the start-up voltage generator further comprises a first capacitor coupled between the gate terminal of the second depletion mode transistor and a ground.
7. The AC-DC power converter of claim 6 , wherein the start-up voltage generator further comprises: a first resistor coupled between the second terminal of the first depletion mode transistor and the ground, and a second resistor coupled between the second terminal of the second depletion mode transistor and the ground.
8. The AC-DC power converter of claim 5 , wherein the start-up voltage generator further comprises a third depletion mode transistor configured to generate a third voltage which is a further fraction of the start-up voltage.
9. The AC-DC power converter of claim 8 , wherein the third depletion mode transistor has: a gate terminal coupled to the second terminal of the second depletion mode transistor, a first terminal coupled to receive the rectified voltage, and a second terminal configured to output a voltage which is a sum of the first through third voltages.
10. The AC-DC power converter of claim 9 , wherein the start-up voltage generator further comprises: a first capacitor coupled between the gate terminal of the second depletion mode transistor and a ground, a second capacitor coupled between the gate terminal of the third depletion mode transistor and the ground, and first through third resistors each coupled between the ground and the second terminal of the corresponding first through third depletion mode transistors.
11. A start-up circuit for a power converter, the start-up circuit comprising: an input node configured to have a first voltage, an output node, and a reference node; and n cascades coupled in series, where n is a positive integer greater than 1, each of the cascades comprising a depletion mode transistor having a first terminal, a second terminal, and a gate terminal, the first terminal of each depletion mode transistor being coupled to the input node, thereby having the first voltage, wherein the second terminal of the depletion mode transistor in the first cascade is coupled to the output node, the second terminal of the depletion mode transistor in the i th cascade is coupled to the gate terminal of the depletion mode transistor in the (i-1) th cascade, where i is a positive integer from 2 to (n-1), and the gate terminal of the depletion mode transistor in the n th cascade is coupled to the reference node.
12. The start-up circuit of claim 11 , wherein each of the cascades further comprises a resistor coupled between the reference node and the second terminal of the corresponding depletion mode transistor.
13. The start-up circuit of claim 12 , wherein each of the second through n th cascades further comprises a capacitor coupled in parallel with the corresponding resistor.
14. The start-up circuit of claim 11 , wherein each of the second through n th cascades further comprises a capacitor coupled between the reference node and the second terminal of the corresponding depletion mode transistor.
15. The start-up circuit of claim 11 , wherein the depletion mode transistors are depletion mode field-effect transistors (FET).
16. The start-up circuit of claim 15 , wherein the FETs are N-channel depletion mode FETs.
17. The start-up circuit of claim 11 , wherein each of the depletion mode transistors has a negative threshold voltage, the start-up circuit configured to generate at the output node an output voltage equal to a sum of the threshold voltages of the depletion mode transistors.
18. A method of starting-up a power converter, the method comprising: generating an AC rectified voltage at an input node upon power-up of the power converter; generating, by a plurality of depletion mode transistors coupled in cascade, a start-up voltage from the rectified voltage, each depletion mode transistor of the plurality of depletion mode transistors receiving the rectified voltage at the input node; and supplying the start-up voltage to a controller of the power converter to provide power for operation of the controller before an output stage of the power converter starts outputting power.
19. The method of claim 18 , wherein the depletion mode transistors are depletion mode field-effect transistors (FET).
20. The method of claim 18 , wherein the start-up voltage is equal to a sum of threshold voltages of the depletion mode transistors.
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February 20, 2013
September 20, 2016
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